1. Field of the Invention
The present invention relates to an active noise control apparatus for controlling the noise in the passenger compartment of a vehicle, and more particularly to an active noise control apparatus having a mixer for mixing canceling signals output from a plurality of active noise controllers into a mixed canceling signal.
2. Description of the Related Art
Noise types that have heretofore been known as occurring in the passenger compartments of vehicles include a muffled sound caused by the combustion of fuel by the engine (hereinafter referred to as “muffled engine sound”), a muffled sound caused by unbalanced rotation of a drive-system rotational member such as a propeller shaft while the vehicle is traveling (hereinafter referred to as “muffled propeller shaft sound”), and a noise transmitted from the road through road wheels and suspensions (hereinafter referred to as “road noise”).
In order to reduce these noises, a canceling signal for canceling the muffled engine sound and a canceling signal for canceling the road noise are generated by respective active noise controllers (see Japanese Laid-Open Patent Publication No. 07-104767, Japanese Laid-Open Patent Publication No. 10-214119, Japanese Laid-Open Patent Publication No. 2009-057018, and Japanese Laid-Open Patent Publication No. 2009-292201).
In view of cost, space, and other factors, a speaker used as the music sound output unit of a music sound device in the passenger compartment is shared as a canceling sound output unit.
The canceling signal for canceling the muffled engine sound and the canceling signal for canceling the road noise are mixed or added into a mixed canceling signal by a mixer, and the mixed canceling signal is supplied to the speaker, which outputs a canceling sound.